Stable aqueous dispersions comprising complexed starch

ABSTRACT

This invention relates to a stable aqueous disersion suitable for application to different substrates and especially to paper substrates for producing a barrier layer against compounds of the saturated and aromatic hydrocarbon type. The said aqueous dispersion are characterised in that they comprise destructurized starch in a complexed form. The present invention refers also to the use of said aqueous dispersion as a coating composition for paper based substrates, as microencapsulant of fragrances and as film-forming component for paints.

This invention relates to a stable aqueous dispersions suitable amongother as coating composition for application to different type ofsubstrates and especially for paper substrates producing a barrier layeragainst compounds of the saturated and aromatic hydrocarbon type such asfor example the compounds commonly known as MOSH (Mineral Oil SaturatedHydrocarbons) and MOAH (Mineral Oil Aromatic Hydrocarbons). Theseaqueous dispersions are characterised in that they comprisedestructurized starch in a complexed form. The use of recycled paperproducts has become increasingly important in the food packaging sectorover the last few years. In fact to reduce the costs associated with thesupply of raw materials, use of these materials through the recycling ofpaper and board wastes makes it possible to reduce the problemsassociated with disposal of the latter, as well as to reduce pollutiondue to incineration.

In order to be effectively used in the food packaging sector recycledpaper products do however require surface treatments to create a barrierlayer against various compounds, for example saturated and aromatichydrocarbons.

Surface treatments make it possible to preserve foodstuffs safely,avoiding contamination.

It is in fact known that dry foodstuffs packed in recycled cardboardpackaging may contain traces of saturated and aromatic hydrocarbons. Thepresence of these compounds is mainly due to the fact that the paper andboard wastes used as a raw material in the production of recycledcardboard largely comprise newspaper, which is commonly printed withinks containing the said compounds, commonly referred to as “Mineral OilSaturated Hydrocarbons” (MOSH) and “Mineral Oil Aromatic Hydrocarbons”(MOAH).

Coating compounds based on starch that can be applied to papersubstrates are currently known in the literature and in commerce.

For example, in Maxwell C. S. “Effect of Ethylene Copolymer-StarchBlends on Water Resistance of Paper”, Tappi 53 (8): 1464-1466 (1970),aqueous dispersions containing gelatinised starch and the ammonium saltof poly(ethylene-acrylic acid) are used to coat paper. These dispersionsare however extremely viscous, even when the solids content is low, andthis greatly reduces the possibility of uniformly depositingsufficiently large quantities of coating composition to allow theformation of a layer which will act as a barrier against theabove-mentioned compounds. Such dispersions have a further disadvantagethat gelatinised starch, which undergoes the phenomenon ofretrogradation, precipitates out in the form of gels, making the processof deposition on paper appreciably more complex.

Starting from the technical problem described above it has now beensurprisingly discovered that by using destructurized starch in complexedform it is possible to make stable aqueous dispersions having a highsolids content capable of producing uniform barrier layers which areresistant to saturated and aromatic hydrocarbons.

This invention in fact relates to an aqueous dispersion suitable fordifferent applications particularly as coating composition for papersubstrates characterised in that it comprises destructurized starch in aform complexed with at least one polymer containing groups of differenthydrophilicity intercalated in the backbone or outside the backbone,said dispersion having dynamic viscosity of 10-500 mPa*s, preferably of30-300 mPa*s, and a solid content of 5-55% by weight, preferably of12-50% by weight.

The destructurized starch, in a form complexed with at least one polymercontaining groups of different hydrophilicity intercalated in thebackbone or outside the backbone, in fact disperses uniformly in waterforming a dispersion of particles which shows particularly stablephysical properties, in particular as regards dynamic viscosity.

In the meaning of this invention, appreciably stable dynamic viscositymeans that the dynamic viscosity of the aqueous dispersion of thecomposition varies by less than 20%, preferably less than 10% afterbeing allowed to stand without stirring for 14 days at 30° C. and thenbeing stirred again for approximately 10 seconds.

This characteristic is particularly advantageous in the paper coatingsector, in which coating compositions are generally deposited in theform of aqueous dispersions, as it eliminates the need to prepare thedispersion immediately prior to use. The aqueous dispersion according tothe invention may be advantageously applied as coating composition onpaper substrates.

The present invention refers also to the use of this aqueous dispersionto produce barrier layers against saturated and aromatic hydrocarboncompounds.

With regards to the dynamic viscosity, it can be measured on the aqueousdispersions according to the present invention by means of a Haake VT500 viscosimeter (or another viscosimeter of equal performances)equipped with a MV-I rotor at 30° C. and 45 rpm.

With regards to the solid content, it can be measured by weighing afterdrying up the aqueous dispersion to constant weight. In this regard, theaqueous dispersion according to the present invention may be placed intoa thermobalance (i.e. Mettler Toledo HB-43-S Halogen thermogravimetricanalyzer) at 140° C. for 30 minutes.

One particularly important aspect of the composition according to thisinvention lies in the fact that it is possible to adjust its dynamicviscosity either by varying the solids content within the rangeindicated above and also by reducing the molecular weight of thedestructurized starch through chemical treatment, preferably with acidsor bases, or through treatment with enzymes, while maintaining thestructure of the dispersion. In the case of acid treatments the use ofstrong acids such as for example sulphuric acid is particularlypreferred. The possibility of adjusting the dynamic viscosity of aqueousdispersions according to this invention makes it possible to use themunder the conditions of use of conventional machines withoutmodifications.

For example, for application on paper substrates dynamic viscosityvalues not in excess of 600 mPa*s are particularly advantageous.

Thanks to the combination of stable physical properties and dynamicviscosity, the stable aqueous dispersion according to this invention canalso advantageously be used as a biodegradable filler in other sectorssuch as for example that of the production of rubbers, such as forexample SBR (styrene-butadiene rubber), polybutadiene, poly-isoprene,EPDM (ethylene propylene diene monomer) rubbers, and natural rubbers.

The stable aqueous dispersion according to this invention can alsoadvantageously be used as a film-forming component for paints, forexample those which allow greater water vapour transpiration, and as avehicle (known as a carrier) for active ingredients in various fieldssuch as for example the pharmaceutical field (drugs), the agriculturalfield (insecticides and herbicides), cosmetics, biotechnology (fixing ofenzymes or other forms of catalysts or microorganisms) or as amicroencapsulant for fragrances in the food industry, pigments or labilesubstances (for example hydroperoxides) to increase their useful life.

Uses of the dispersion according to the invention as biodegradablefiller for the production of rubbers, as film-forming component forpaints and as a microencapsulant for fragrances are particularlypreferred.

In a preferred embodiment the stable aqueous dispersion according tothis invention comprises, with respect to the total weight of thedispersion:

-   -   45-95% by weight, preferably 50-88% by weight of water,    -   5-55% by weight, preferably 12-50% by weight, of a starch-based        composition comprising, with respect to the total weight of the        starch-based composition:        -   i) 30-90% by weight, preferably 50-80%, of destructurized            starch;        -   ii) 10-70% by weight, preferably 20-50%, of at least one            polymer containing groups of different hydrophilicity            intercalated in the backbone or outside the backbone;        -   iii) 0-25% by weight, preferably 0-20%, of plasticizers.

In the meaning of this invention, destructurized starch means starch ofany kind which has substantially lost its native granular structure andis substantially free of granular structure residues. In the presentinvention, a destructurized starch which has lost its native granularstructure and is free of granular structure residues is preferred. Inthis connection, the disclosure of EP 0 327 505 and EP 0118 240 isincorporated herein as reference. As far as the native granularstructure of starch is concerned, this can advantageously be identifiedby phase contrast optical microscopy at 400× magnifications.

The content of residual granular structures and residues of the starchmay be analyzed by means of a Brabender Viscograph-E Belotti amilographunder the following conditions:

Dry content: 23.1%Temperature profile: Initial temperature (° C.)=25° C., heating rate (°C./min)=1.5 Peak Temperature=85° C.; Isothermal Step=30′, cooling rate(° C./min)=1.5; Final Temperature (° C.)=25

Rpm=70

In the composition according to this invention, the content of starchresidual granular structures and residues can lead to a maximum value ofBraebender Units reached at the end of the above temperature profile<200, preferably <100 and more preferably <60 at a 23.1% of dry content.

The starch which can be used to prepare the stable aqueous dispersionaccording to this invention is native starch, such as for example maizestarch, potato starch, rice starch, tapioca starch or starch which hasbeen physically or chemically modified such as for example ethoxylatedstarch, starch acetate or starch hydroxypropylate, cross-linked starch,oxidised starch, dextrinised starch, dextrin and mixtures thereof.Particularly preferred is starch from maize, potato and mixturesthereof.

In the meaning of this invention, destructurized starch in complexedform means destructurized starch which shows one or more crystallineforms in an X-ray spectrometer which can be associated with one or moreof the diffraction peaks listed below.

Crystalline form V_(H) V_(A) E_(H) (2θ) (2θ) (2θ)  7.4 (±0.3)  7.7(±0.3)  7.0 (±0.2) 12.8 (±0.2) 13.5 (±0.4) 12.0 (±0.3) 16.7 (±0.2) 15.7(±0.1) 13.1 (±0.3) 18.3 (±0.2) 17.6 (±0.1) 18.2 (±0.4) 19.7 (±0.3) 19.3(±0.2) 24.9 (±0.2) 22.2 (±0.2) 20.8 (±0.2) 24.9 (±0.2) 23.7 (±0.1) 26.4(±0.1) 27.5 (±0.1) 28.6 (±0.1)

It is well known that the crystalline forms of the complexed starch maypass from one form to another over time, due to their differentthermodynamic stability.

In the dispersions according to the presence invention, the presence ofdestructurized starch in a complexed form provides for the dynamicviscosity range above disclosed.

Said polymers containing groups of different hydrophilicity intercalatedin the backbone or outside the backbone are preferably insoluble inwater. When the aqueous dispersions according to the present inventionare applied as coating compositions on paper substrates, this makes itpossible to render paper substrates water resistant. The polymers can bewater dispersible. The meaning of the present invention, groups ofdifferent hydrophilicity show different Hansen solubility parameters.

The said polymers with groups of different hydrophylicity intercalatedoutside the backbone are advantageously selected from:

-   -   copolymers of ethylene with vinyl alcohol, acrylic acid and its        salts, methacrylic acid and its salts, crotonic acid, itaconic        acid and their salts, maleic anhydride, glycidyl methacrylate        and mixtures thereof;    -   vinyl acetate/vinyl alcohol copolymers, preferably with <55% by        moles of vinyl alcohol units in blocks;

The said polymers with groups intercalated in the backbone areadvantageously selected from:

-   -   aliphatic polyurethanes, aliphatic and aliphatic/aromatic        polyesters, preferably comprising repeating units of diacid or        hydroxyacids with 6-20 carbon atom in the main chain, random or        block polyurethane/polyether, polyurethane/polyester,        polyamide/polyester, polyester/polyether, polyurea/polyester,        polyurea/polyester copolymers, polycaprolactone/urethane, in        which the molecular weight of the polycaprolactone blocks is        between 300 and 3000.

Mixtures of the said polymers may also be used.

In case of polymers not water dispersible such as the ones with groupsof different hydrophilicity intercalated in the backbone, thestarch-based composition advantageously comprises polymers with morehydrophilic groups outside the backbone in a percentage 1-50% by weightrelated to the total polymeric component which act as dispersing agent

Among the polymers containing groups of different hydrophilicity theones with more hydrophilic groups intercalated outside the backbone arepreferred.

Of these, copolymers of ethylene with vinyl alcohol and/or with acrylicacid are particularly preferred.

In the case of copolymers of ethylene with vinyl alcohol, thesepreferably contain 20-50% in moles of ethylene units.

In the case of ethylene copolymers with acrylic acid, these preferablycontain 70-99% by weight of ethylene units.

Plasticizers are preferably selected from polyols having 2 to 22 carbonatoms, and among these polyols having 1 to 20 hydroxyl groups containing2 to 6 carbon atoms, their ethers, thioethers and organic and inorganicesters are particularly preferred.

Examples of plasticisers are glycerine, diglycerol, polyglycerol,pentaerythritol, ethoxylated polyglycerol, ethylene glycol, polyethyleneglycol, 1,2-propandiol, 1,3-propandiol, 1,4-butandiol, neopentyl glycol,sorbitol monoacetate, sorbitol diacetate, sorbitol monoethoxylate,sorbitol diethoxylate, and mixtures thereof.

The aqueous dispersion according to this invention may also containadditives, for example fillers, dispersants, cross-linking agents,surfactants, antifoaming agents, suspension agents, densifiers,preservatives, pigments and dyes.

As far as fillers are concerned, these may be inorganic and/or organic.Particularly preferred examples of inorganic fillers are: talc, clays,silica, mica, kaolin, titanium dioxide and wollastonite. Preferredorganic fillers are derivatives of raw materials of renewable originsuch as for example cellulose fibres. Fillers can be nanostructured.

Surfactants are advantageously selected from anionic, cationic andnon-ionic surfactants. Cationic surfactants generally consist of a bulkycation often containing a long alkyl chain (for example a quaternaryammonium, a phosphonium or sulphonium salt). In most cases the anion isthe chloride, sulphate or nitrate ion. Anionic surfactants generallyconsist of alkyl, aryl, alkyl aryl, styryl, di- or tristyrylsulphonates, sulphates, phosphates, phosphonates, dithiocarbamates,carboxylates generally neutralised by alkaline or alkaline earth metals,amines or alkanolamines.

Examples of non-ionic surfactants are products belonging to the classesof polyethoxylated esters and ethers, alkyl polyglucosides, derivativesof sorbitol and saccharose, fatty acid esters or amides, fatty acidmono- and diglycerides, ethoxylated alkyl phenols, di- or tristyrylphenol ethoxylates, ETO-propoxylate block copolymers.

Examples of antifoaming agents include silicone antifoaming agents andsalts of fatty acids. Pigments and dyes or colour stabilisers may alsobe added as necessary, for example titanium dioxide, clays, calciumcarbonate, talc, mica, silica, silicates, iron oxides and hydroxides,carbon black and magnesium oxide.

According to the present invention, the starch-based compositioncomprising starch and at least one polymer containing groups ofdifferent hydrophilicity intercalated in the backbone or outside thebackbone can be obtained by the processes of extruding a molten mixturewith the provision of specific energy in excess of 0.15 kWh/kg duringthe said extrusion.

Preparation of the starch-based composition by extrusion takes place atfor example temperatures between 120 and 210° C., and preferably between140 and 190° C. Extruders which are suitable for use for preparing thecomposition according to this invention are mono and twin screwextruders. Twin screw extruders are preferred. The twin screw extrudershaving screws with mixing zones with highly working elements are morepreferred. Mixing zones with “reverse” profile are also particularlysuitable.

The preparation process of the stable aqueous dispersion according tothe present invention, comprises the steps of:

-   -   (i) feeding the starch-based composition comprising starch in a        form complexed with at least one polymer containing groups of        different hydrophilicity intercalated in the backbone or outside        the backbone to a dispersing machine equipped with a vessel and        a stirring system comprising at least one rotor and at least one        stator;    -   (ii) dispersing the starch-based composition in water by        stirring vigorously with tangential speeds of from 10 s⁻¹ to 50        s⁻¹ until the dispersion is homogeneous and reaches a constant        value of dynamic viscosity, and optionally    -   (iii) regulating the aqueous dispersion solid content by adding        or removing (e.g. by evaporation) the proper amount of water to        reach a solid content of 5-55% by weight, preferably 12-50% by        weight.

Examples of dispersing machines suitable to prepare the aqueousdispersion according to the present invention are high shear mixers,homogenizers such as IKA Ultra-Turrax T25 and IKA DR2000/1. Thepreparation process of the aqueous dispersion may be performed in batchor in continuous.

In step (i) the starch-based composition may be fed to the dispersingsystem in pellet or powder form. The powder may be obtained by grindingthe pellets.

In the preparation of the aqueous dispersion according to the inventionbetween step (i) and (ii) the starch-based composition may be left understirring at 1500-3000 rpm for 20-80 minutes (so-called wetting time).

During step (ii), acids, bases or enzymes can be advantageously addedfollowed by neutralisation. In the case of acid, the use of strong acidssuch as for example sulphuric acid in an amount of 0.1-2% by weight,preferably 0.2-1% by weight, is particularly preferred. In this case,neutralization may be performed with alkaline compounds such as forexample NaOH, NH₄OH, Ca(OH)₂.

The stable aqueous dispersion according to this invention may be appliedto paper substrates using any of the processes known to those skilled inthe art. Preferably the aqueous dispersion will be applied using forexample blade or film methods for coating paper.

Said coating processes comprise the steps of:

-   -   i. applying on at least one face of said paper substrate a layer        of the aqueous dispersion according to the invention as a        coating composition;    -   ii. drying said paper substrate comprising at least one layer of        the coating composition.

Regarding the application step, it can be advantageously usedapplication systems with one or more applicator rolls (e.g. size press,film press), with jets (e.g. jet flow), with offset-print or anycombination thererof. Between steps (i) and (ii), the coating processcan furthermore advantageously comprise the partial removal of theapplied coating composition from the paper substrate, thus allowing theadjustment of grammage at the same time levelling the thickness of thecoating layer. Said removal can advantageously be performed by means ofone or more metal blades, by means of one or more air jets (so-calledair-blade technology) or by mean of one or more air blade (so-calledair-knife technology) or any combination thereof.

As far as the drying step of the coated paper substrate is concerned, itcan be advantageously performed by means of radiation systems,preferably with infra-red radiations, convection systems, preferablywith hot air, or contact systems, preferably with drying rollers, or anycombination thereof.

In a preferred embodiment, the present invention refers to a coatingprocess comprising the steps of:

-   -   i. applying on at least one face of said paper substrate a layer        of the aqueous dispersion according to the present invention as        a coating composition by means of one or more applicator rolls,    -   ii. removing part of the coating composition applied on the        paper substrate by means of one or more air-knifes;    -   iii. drying, by means of radiation, convection, contact or any        combination thereof, said paper substrate comprising at least        one layer of said coating composition.

The present invention refers also to the coating composition obtainablewith the above process.

The paper laminate obtained with the above disclosed coating processescomprises at least one substrate of the paper type and at least onelayer of the coating composition according to the present invention.Thanks to the characteristics of the aqueous dispersion according to theinvention this laminate has a uniform layer of coating and high barrierproperties against saturated and aromatic hydrocarbon compounds, whichmakes it particularly useful for the manufacture of packaging in thefood sector.

The said paper laminate may also advantageously be subjected to furtherextrusion coating and/or extrusion lamination treatments withbiodegradable polymer materials such as for example the polyestersdescribed in patent application WO 2009/118377, to form a particularlyeffective barrier layer against water which also renders the saidlaminate suitable for the packaging of liquids and various types offoods such as among others meat, ice cream, yoghurt and foods which areparticularly sensitive to oxidation and/or moisture such as toasts,coffee and potato chips.

In the meaning of this invention the term “paper substrate” hereincludes all materials comprised of vegetable fibre raw materials, forexample cellulose fibres. Suitable examples are paper-based substratesamong which paper sheets and cardboards with a basic weight from 10 to1000 g/m² are particularly preferred.

In a preferred embodiment the coating composition is biodegradable andtherefore particularly suitable for the manufacture of laminated paperproducts which are biodegradable by composting according to standard EN13432.

FIG. 1 shows a phase contrast microscopy photograph of the dispersionaccording to Example 5.

FIG. 2 shows a 150×SEM photograph of the cardboard according to Example7.

FIG. 3 shows a 150×SEM photograph of the cardboard according to Example8.

FIG. 4 shows a 150×SEM photograph of a cardboard without any coatingcomposition.

This invention will now be illustrated with reference to somenon-limiting examples.

EXAMPLE 1

56.3 parts of native maize starch (containing 12% by weight of water),24.8 parts of polyethylene acrylic acid containing 20% by weight ofacrylic acid, 7.9 parts of glycerine and 10.1 parts of water have beenfed to an OMC twin screw extruder in accordance with the followingoperative conditions:

thermal profilefeed zone (° C.): 60extrusion zone (° C.): 145−170−180×4−150×2throughput (kg/h)=40SME (specific energy) (kWh/kg)=0.232

EXAMPLE 2

49.6 parts of native maize starch (containing 12% by weight of water),27.5 parts of polyethylene vinylalcohol containing 38% by mole ofethylene, 4.6 parts of polyethylene acrylic acid containing 20% byweight of acrylic acid, 7.2 parts of glycerine and 11.4 parts of waterhave been fed to a TSA twin screw extruder in accordance with thefollowing operative conditions:

thermal profilefeed zone (° C.): 70extrusion zone (° C.): 70-180×5-160throughput (kg/h)=3SME (specific energy) (kWh/kg)=0.199

The compositions according to Examples 1 and 2 have been grounded up at25° C. and sieved to a particle size of <250 μm and analysed in aPhilips X′Pert θ/2θ x-ray spectrometer using a Bragg-Brentane geometry,using X Cu K_(α) radiation with λ=1.5416 Å and a power of 1.6 kW. Theangular range used was from 5 to 60° (2θ) with steps of 0.03° (2θ) andan acquisition time of two seconds per step.

Analysis of the X-ray pattern revealed the presence of diffraction peaksshown in table 1 indicating formation of the complex between the starchand the polymers containing hydrophobic groups intercalated withhydrophobic sequences (E_(H), V_(H) and V_(A) forms).

TABLE 1 diffraction peaks of the Compositions according to Examples 1and 2 Example 1 (2θ) Example 2 (2θ)  6.8 — 11.8 — — 12.7 13.1 — 18.1 —20.7 —

The compositions according to Example 1 and 2 have been grounded up at25° C. and sieved to a particle size of <250 μm have been analyzed bymeans of a Brabender Viscograph-E Belotti amilograph under the followingconditions:

Dry content: 23.1%Temperature profile: Initial temperature (° C.)=25° C., heating rate (°C./min)=1.5 Peak Temperature=85° C.; Isothermal Step=30′, cooling rate(° C./min)=1.5; Final Temperature (° C.)=25

Rpm=70

Viscosity of Example 1 and 2 in terms of Brabender Units (BU) arerespectively of 8 and 6 BU.

COMPARATIVE EXAMPLE 1

15.2 g of sodium hydroxide (≧97%, Fluka) have been dissolved into 700 mlof deionised water at 95-100° C. under stirring, in a 1 l conical flaskequipped with a condensing system. Once all the sodium hydroxide isdissolved, 70 g of poly(ethylene-co-acrylic acid) (EAA—20% by weight ofacrylic acid) Dow Primacor 59801 have been added keeping the system inthe same conditions (stirring, temperature and condenser) leaving areaction time of three hours. The solution is then let to cool down upto 50-60° C. and discharged into aluminium vessels. The aluminiumvessels have been put into an oven at 60° C. for 12 hours in order toremove the excess of water and then the obtained salt has been removedby scratching it from the aluminium vessels using a steel spatula. Thewater content of the obtained salt has been measured by means ofthermogravimetrical analysis (Perkin Elmer TGA 7) at 120° C. for 2 hoursresulting 9.3%.

7.48 g of EAANa have been dissolved into 400 ml of deionised water at50° C. and the solution has been then let cooling down to ambienttemperature. An amount of 17 g of native corn starch has been added tothe solution and put into a Brabender Viscograph-E Belotti under thefollowing conditions:

Temperature profile: Initial temperature (° C.)=25° C., heating rate (°C./min)=1.5 Peak Temperature=85° C.; Isothermal Step=30′, cooling rate(° C./min)=1.5; Final Temperature (° C.)=25

Rpm=70

The viscosity of Comparative Example 1 in terms of Brabender Units (BU)at the end of the cycle is approximately 70 BU.

COMPARATIVE EXAMPLE 2

12.2 g of EAANa prepared according to Comparative Example 1 have beendissolved into 400 ml of deionised water at 50° C. and the solution hasbeen then let cooling down to ambient temperature. An amount of 41.4 gof native corn starch has been added to the solution and put into aBrabender Viscograph-E Belotti under the following conditions:

Temperature profile: Initial temperature (° C.)=25° C., heating rate (°C./min)=1.5 Peak Temperature=85° C.; Isothermal Step=30′, cooling rate(° C./min)=1.5; Final Temperature (° C.)=25

Rpm=70

The viscosity of Comparative Example 2 in terms of Brabender Units (BU)at the end of the cycle is approximately 250 BU.

EXAMPLES 3 TO 6

The compositions according to Example 1 and 2 have been water dispersedusing the procedures listed in Table 2.

TABLE 2 procedures for preparing the dispersions according to Examples 3to 6 Example 3 Example 4 Example 5 Example 6 Machine IKA Ultra- IKAUltra- IKA IKA Turrax T25 Turrax T25 DR2000/10 DR2000/10 Recirculatingsystem no no yes yes Grinding and sieving <400 μm no no yes yes Wettingtime (under stirring) before dispersion (min) — — 60 60 Compositionaccording to Example 1 (kg) 0.01 0.04 31 — Composition according toExample 2 — — — 20 water (kg) 0.1 0.1 72 80 water/sulfuric acid (96%)50/50 (m/m) solution (kg) 0.002 0 2.1* 0 Tangential speed (s⁻¹) 24 24 2828 Vessel Volume (dm³) 0.25 0.25 150 150 Steady stirring revolutionspeed (1/min) 24000 24000 5040 5040 Stirring time(min) 20 20 150 180Initial temperature (° C.) 25 25 30 30 Final temperature (° C.) 80 85 9096 *the solution was added after 90 minutes of stirring

The dispersions according to example 3 and 5 have been neutralised with50% m/m sodium hydroxide solution.

The dispersions according to example 3 to 6, appeared milky and withoutlumps.

The dispersions according to Examples 3 to 6 and Comparative Examples 1and 2 have been characterized by dynamic viscosity, melt viscosity,Phase Contrast Optical Microscopy and X-ray diffraction (of the drieddispersion).

The dynamic viscosity of Example 3 (approximately 9% of dry content) andExample 5 (approximately 30% of dry content) and of Comparative Example1 (approximately 5.5% of dry content) and Comparative Example 2(approximately 9% of dry content) has been analyzed over a period of twoweeks by means of an Haake VT 500 viscometer equipped with an MV-I rotorat 30° C. and 45 rpm. All the aged sample have been previously shackedfor 10 seconds in order to homogenize them.

TABLE 3 dynamic viscosity (mPa * s) over time Comparative ComparativeTime (gg) Example 1 Example 2 Example 3 Example 5 0 162 623 72 133 1 144615 70 131 2 145 620 72 129 3 140 605 72 132 7 134 334 70 134 14 120 31072 133

While Comparative Examples 1 and 2 show a decreasing viscosity duringthe two weeks period that is especially remarkable for ComparativeExample 2 (higher dry content), the viscosity of Example 3 and Example 5remains constant.

It has to be highlighted that Comparative Example 1 has approximatelythe same viscosity of Example 5 but with a solid content of 5.6% against30%. On the contrary, Comparative Example 2, having the same solidcontent of Example 3, shows a dynamic viscosity one order of magnitudehigher. This is a focal point in order to obtain a significant basicweight of barrier material with a single deposition step keeping theviscosity at a low level, suitable for industrial deposition.

The dispersions according to Examples 4 and 5 have been dried by castingat air at ambient temperature and pelletized. About 30 g of these drieddispersions has been conditioned to a water content of 6.6% (measured byweight loss after 2 h at 120° C.) and a rheological flow curve has beenobtained by means of a Gottfert RT2000/V capillary rheometer accordingto ASTM D-3835 (at T=180° C., L/D=10).

TABLE 4 melt viscosity Example 4 Example 5 η (Pa * s) η (Pa * s) Initialshear rate (s⁻¹) = 6100 344 7.2 Final shear rate (s⁻¹) = 481 35 292

The dried dispersion according to Example 4, where acid is not used,shows a pseudoplasic flow curve trend with viscosity value of an orderof magnitude higher than Example 5_where acid is used. This shows how itis possible to adjust the viscosity of the dispersions by reducing themolecular weight of the destructurized starch.

Phase contrast optical microscopy has been performed on the dispersionaccording to Example 5 by means of a Leitz Wetzlar Orthoplan model phasecontrast optical microscope using the following parameters:magnification 400×, objective EF 40/0.65 Phaco 2, phase ring no. 5. Adrop of dispersion has been placed on a microscopic glass with a Pasteurpipette and observed after having placed another microscopic glass ontoit and thinned the thickness with a gentle pressure. The dispersionproved to be free of any residues with a granular structure that couldbe attributed to native starch or to granular starch residues, thusproviding evidence of the destructurized nature of the starch (see FIG.1)

X-ray diffraction of the dried dispersion according to Example 5 andComparative Example 1 has been performed by means of a Philips X′Pertθ/2θ x-ray spectrometer equipped with a Bragg-Brentano geometry, using XCu K_(α) radiation with λ=1.5416 Å and a power of 1.6 kW. The angularrange used was from 5 to 60° (2θ) with steps of 0.03° (2θ) and anacquisition time of two seconds per step.

Analysis of the X-ray pattern revealed the presence of diffraction peaksshown in table 5 indicating loss of native starch crystallinity andformation of the complex between the starch and the polymers containinghydrophobic groups intercalated with hydrophobic sequences (V_(H)).

TABLE 5 diffraction peaks of the dispersion according to Example 5 andComparative Example 1 Example 5 (2θ) Comparative Example 1 (2θ) 12.9 — —18.5 19.7 —

In this case, it can be highlighted that the diffraction peaks presentin the dried dispersion according to Example 5, differs from thediffraction peaks detected for the composition according to Example 1.Without willing to be bound to any theory, it is believed that thischange in the diffraction peaks distribution is linked to the transitionfrom a crystalline form to another during the preparation of thedispersion.

EXAMPLE 7

A recycled cardboard sheets of A4 size of 450 μm thickness has beencoated in a single deposition step with approximately 10 ml ofdispersion according to Example 5 by means of a pipette and removing theexcess of dispersion by rolling a steel rod long 40 cm and having adiameter of 7 mm. Straight after deposition, the cardboard has been putin an oven at 200° C. for 30 s for drying it.

Then it has been let to condition at ambient temperature overnight.

A basic weight of dry coating of approximately 15 g/m² has been obtainedwith a single deposition step.

EXAMPLE 8

A recycled cardboard sheets of A4 size of 450 μm thickness has beencoated in a single deposition step with approximately 10 ml ofdispersion according to Example 6 by means of a pipette and removing theexcess of dispersion by rolling a steel rod long 40 cm and having adiameter of 7 mm. Straight after deposition, the cardboard has been putin an oven at 200° C. for 30 s for drying it.

Then it has been let to condition at ambient temperature overnight.

A basic weight of dry coating of approximately 13 g/m² has been obtainedwith a single deposition step.

The coated cardboards according to Example 7 and 8 have been cut intoapproximately 30 pieces of nearly 8×3 cm. A pair of pieces has been sunkfor half of their length in a 100 ml becker filled with deionised waterfor nearly 5 seconds. Then the sunk coated faces of one piece has beenslightly scratched for a few seconds to the sunk coated face of theother piece and mostly of the coating has been moved from the cardboardinto the water. This operation has been repeated on the other half ofthe two pieces for all the 30 pieces.

The water has been removed by a gentle air flow under mild heating (i.e.60° C.) and a final drying step has been performed in an oven at 120° C.for 2 hours.

At the end of this step an amount of approximately 500 mg to 1 g of drycoating has been obtained which once pulverized with mortar and pestlehas been analyzed by X-ray diffraction by means of a Philips X′Pert θ/2θx-ray spectrometer using a Bragg-Brentano geometry, using X Cu K_(α)radiation with λ=1.5416 Å and a power of 1.6 kW. The angular range usedwas from 5 to 60° (2θ) with steps of 0.03° (2θ) and an acquisition timeof two seconds per step.

Analysis of the X-ray pattern revealed the presence of diffraction peaksshown in table 7 indicating of the presence of the complex between thestarch and the polymers containing hydrophobic groups intercalated withhydrophobic sequences (V_(H) and V_(A)).

TABLE 7 diffraction peaks of the coating composition after removal fromthe cardboard Example 7 (2θ) Example 8 (2θ) 13.1 12.8 19.6 19.6 20.8

This shows that the diffraction peaks of the complexed starch aredetectable after removal from the cardboard of the coating composition.

A piece of 5×5 mm size of the cardboards according to Example 7, 8 anduntreated cardboard has been gold coated by means of an Agar B7341sputter coater at a current strength of 40 mA for 40 seconds.

Then the samples have been analysed using a Zeiss Supra 40 scanningelectron microscope with the following operative conditions:

magnification: 150−1000×(with reference to Polaroid standard 545)accelerating voltage=10 kVworking distance=approximately 5 mm

The cardboards coated according to Example 7 (see FIG. 2) and 8 (seeFIG. 3) show a uniform surface, i.e. a substantially complete coverageof the surface cellulose fibres present on the surface of the untreatedcardboard (see FIG. 4)

Determination of the Barrier Effect Against Saturated and AromaticHydrocarbons of the Dispersion According to Example 5 Preparation of thePolluting Solutions

-   PS1: a solution made of (w/w): Hexadecane (Sigma-Aldrich Reagent    Plus 99%) 92.0%, Phenanthrene (Acros Organics 97%) 6.6%, Hexacosane    (hereinafter “C26H54”) (Aldrich 99%) 1.7% has been prepared in a 20    ml flask under stirring at 70° C. for 3 hours.-   PS2: a solution made of (w/w): Toluene (Sigma-Aldrich Chromasolv    99.9%) 99.29%, Perylene (Fluka 97%) 0.47%, C26H54 (Aldrich 99%)    0.24% has been prepared in a 20 ml flask under stirring at 80° C.    for 3 hours.

Preparation of Polluted Cardboards

-   PC1: 25 μl of PS1 have been added (at approximately 70° C.) by means    of an Hamilton 25 μl microsyringe to a piece of virgin cardboard of    270 μm thickness of 3.5×3.5 cm size and conditioned at ambient    temperature for half an hour.-   PC2: 240 μl of PS2 have been added (at approximately 80° C.) by    means of an ILS 500 μl microsyringe to a piece of virgin cardboard    of 270 μm thickness of 3.5×3.5 cm size. The solution addition has    been made in three steps (3×80 μl) in order to avoid overflowing.    The cardboard has been then conditioned at ambient temperature for    half an hour.-   PC3: a commercial recycled cardboard of 450 μm thickness of 7×7 cm    size has been also taken as further Polluted Cardboard (PC3).

Coating of Polluted Cardboards

a) Coating with the Dispersion According to Example 5

PC1, PC2 and PC3 have been coated in one single step with approximately3 ml of dispersion according to Example 5 by means of a pasteur pipetteremoving the excess of dispersion by rolling a steel rod long 40 cm andhaving a diameter of 7 mm. Straight after deposition, the cardboardshave been put in an oven at 200° C. for 30 s for drying it.

Then they have been let to condition at ambient temperature overnight.

The basic weight of the dry coating has been found to be of 15 g/m²

Test of Migration on Rice (PC1/PC2 Cardboards)

Approximately 6 g of rice (Riso Fino S. Andrea—Italy) have been put intwo different weighing bottles of 55 mm of diameters coveringhomogeneously their bottom.

PC1-Example 5 and PC2-Example 5 have been put inside the weighingbottles with the polluted side facing the rice. In order to assure thecontact between the cardboard and the rice a weight of 56 g over asurface of 23×23 mm has been put on the cardboard.

Then the weighing bottle has been covered and put in an oven at 40° C.for 9 days.

Test of Migration on Activated Charcoal (PC3 Cardboard)

Approximately 9 g of activated charcoal 8-20 mesh (Sigma Aldrich) havebeen put in one weighing bottle of 11 cm of diameters coveringhomogeneously their bottom.

PC3-Example 5 has been put inside the weighing bottle with the pollutedside facing the activated charcoal. In order to assure the contactbetween the cardboard and the activated charcoal a weight of 97 g over acircular surface of 24 cm2 has been put on the cardboard.

Then the weighing bottle has been covered and put in an oven at 70° C.for 24 hours.

Pollutant Extraction from PC1/PC2 Migration Test on Rice

At the end of migration test, activated charcoal or rice have been putinside a 50 ml flask and 20 ml of toluene (Sigma-Aldrich Chromasolv99.9%) have been added. The flask has been heated up to 170° C. understirring with a condensing system and the extraction has been carried onfor 2 hours.

Pollutant Extraction from PC3 Migration Test on Activated Charcoal

At the end of migration test, activated charcoal or rice have been putinside a 50 ml flask and 30 ml of toluene (Sigma-Aldrich Chromasolv99.9%) have been added. The flask has been heated up to 170° C. understirring with a condensing system and the extraction has been carried onfor 2 hours.

Pollutant Extraction from PC1/PC2/PC3 Cardboards (Reference)

In order to have a reference of the amount of MOSH and MOAH inside thecardboards, PC1, PC2 and PC3 have been cut in pieces of about 1.5×1.5 cmand put inside a 50 ml flask and 20 ml of toluene (Sigma-AldrichChromasolv 99.9%) for PC1/PC2 or 30 ml for PC3, have been added. Theflask has been heated up to 170° C. under stirring with a condensingsystem and the extraction has been carried on for 2 hours.

Gas Chromatography—Mass Spectrometry (GC-MS) Analysis

An amount of 1 ml of liquid coming from the extraction has been filteredat 0.2 μl into 1 ml vials and sealed before performing GC-MS analysis inthe following conditions:

Gas-Chromatograph: Thermo Trace GC Ultra;

Column: Phenomenex Zebron ZB-5MSi (length: 30 m−diameter: 0.25 mm;Injector temperature (° C.)=300;Transfer-line temperature (° C.)=280;

Carrier=Helium;

Flow (ml/min)=1;Split Flow (ml/min)=50;

Temperature run:

Isothermal step (° C.−min)=70−4;Temperature scan: T_(m)(° C.)=70−heating rate (° C./min)=15−T_(fin)(°C.)=340;Isothermal step (° C.−min)=340−5;Injection type: splitless;Injection volume (μl)=1;

Mass Spectrometer: Thermo DSQ II;

Source temperature (° C.)=250;Ionization type: ElectronImpact;Scan Type: Polluted cardboard positive ion SIM; Recycled Cardboard: FullScanPeak detection for polluted cardboards (D): phenanthrene=178;C26H54=57+366; perylene=252Peak detection for recycled cardboard (D): 33-500

Two repetitions of each sample have been analyzed by GC-MS and resultsare calculated in terms of peak area of the single molecular ion andpercentage of reduction of the interested peak on treated samplescompared to the reference).

For each pollutant, the barrier effect of the coating compositionaccording to the invention has been determined according to thefollowing formula:

${{barrier}\mspace{14mu} {effect}} = {\frac{\left( {P_{reference} - P_{{PCi}\text{-}{Example}\; 5}} \right)}{P_{reference}} \cdot 100}$

Wherein

-   P_(reference)=peak area of the single molecular ion in the reference    cardboard (without coating);-   P_(PCi-Example 5)=peak area of the single molecular ion in the PC1,    PC2 or PC3 cardboard (with coating layer obtained with the    dispersion according to Example 5)

The results of the migration tests are reported in herebelow tables 8-10

TABLE 8 Results of migration on rice with PC1 cardboards Barrier effect(%) phenanthrene 97.3 C26H54 99.8

TABLE 9 Results of migration on rice with PC2 cardboards Barrier effect(%) Perylene 100.0 C26H54 98.8

TABLE 10 Results of migration on activated charcoal with PC3 cardboardsBarrier effect (%) Alkane C23H48 95.8 Alkane C24H50 97.6 Alkane C25H52100.0 Alkane C26H54 99.6 Alkane C27H56 100.0

1. Stable aqueous dispersion wherein it comprises destructurized starchin a form complexed with at least one polymer containing groups ofdifferent hydrophilicity intercalated in the backbone or outside thebackbone, said dispersion having dynamic viscosity of 10-500 mPa*s and asolid content of 5-55% by weight.
 2. Stable aqueous dispersion accordingto claim 1 comprising, with respect to the total weight of thedispersion: 45-95% by weight of water 5-55% by weight of a starch-basedcomposition comprising, with respect to the total weight of thestarch-based composition: i) 30-90% by weight of destructurized starch;ii) 10-70% by weight of at least one polymer containing groups ofdifferent hydrophilicity intercalated in the backbone or outside thebackbone; iii) 0-25% by weight of plasticizers.
 3. Stable aqueousdispersion according to claim 1, wherein said polymers containing groupsof different hydrophilicity intercalated in the backbone or outside thebackbone are selected from: copolymers of ethylene with vinyl alcohol,acrylic acid and its salts, methacrylic acid and its salts, crotonicacid, itaconic acid and its salts, maleic anhydride, glycidylmethacrylate and mixtures thereof; vinyl acetate/vinyl alcoholcopolymers; aliphatic polyurethanes, aliphatic and aliphatic/aromaticpolyesters, random or block polyurethane/polyether,polyurethane/polyester, polyamide/polyester, polyester/polyether,polyurea/polyester, polyurea/polyester copolymers,polycaprolactone/urethane, in which the molecular weight of thepolycaprolactone blocks is between 300 and
 3000. 4. Stable aqueouscomposition according to claim 1, wherein said polymers containinggroups of different hydrophilicity intercalated outside the backbone arecopolymers of ethylene with vinylalcohol and/or with acrylic acid. 5.Stable aqueous dispersion according to claim 4, wherein said copolymersof ethylene with vinyl alcohol contain 20-50% in moles of ethyleneunits.
 6. Stable aqueous dispersion according to claim 4, wherein saidcopolymers of ethylene with acrilic acid contain 70-99% by weight ofethylene units.
 7. Stable aqueous dispersion according to claim 1comprising fillers, dispersants, cross-linking agents, surfactants,antifoaming agents, suspension agents, densifiers, preservatives,pigments.
 8. Process for preparing the stable aqueous dispersionaccording to claim 1, comprising the steps of: i. feeding a starch-basedcomposition comprising starch in a form complexed with at least onepolymer containing groups of different hydrophilicity intercalated inthe backbone or outside the backbone to a dispersing machine equippedwith a vessel and a stirring system comprising at least one rotor and atleast one stator; ii. dispersing the starch-based composition in waterby stirring vigorously with tangential speeds of from 10 s⁻¹ to 50 s⁻¹until the dispersion is homogeneous and reaches a constant value ofdynamic viscosity, and optionally iii. regulating the solid content ofthe aqueous dispersion by adding or removing the proper amount of waterto reach a solid content of 5-55% by weight.
 9. Use of the stableaqueous dispersion according to claim 1 for coating paper basedsubstrates.
 10. Coating process of a paper substrate comprising thesteps of: i. applying on at least one face of said paper substrate alayer of the aqueous dispersion according to claim 1 as a coatingcomposition; ii. drying said paper substrate comprising at least onelayer of said coating composition.
 11. Coating process according toclaim 10 wherein between step (i) and (ii) a part of the coatingcomposition applied on the paper substrate is removed by means of one ormore air-knifes.
 12. Coating process according to claim 10, wherein thedrying of the paper substrate is effected by means of radiation,convection, contact or any combination thereof.
 13. Coating compositionobtainable with the process according to claim
 10. 14. Paper basedlaminate comprising a paper based substrate and at least one layer ofthe coating composition according to claim
 13. 15. Use of the stableaqueous dispersion according to claim 1 as biodegradable filler in theproduction of rubbers.
 16. Use of the stable aqueous dispersionaccording to claim 1 as microencapsulant for fragrances.
 17. Use of thestable aqueous dispersion according to claim 1 as film-forming componentfor paints.
 18. Stable aqueous dispersion according to claim 2, whereinsaid polymers containing groups of different hydrophilicity intercalatedin the backbone or outside the backbone are selected from: copolymers ofethylene with vinyl alcohol, acrylic acid and its salts, methacrylicacid and its salts, crotonic acid, itaconic acid and its salts, maleicanhydride, glycidyl methacrylate and mixtures thereof; vinylacetate/vinyl alcohol copolymers; aliphatic polyurethanes, aliphatic andaliphatic/aromatic polyesters, random or block polyurethane/polyether,polyurethane/polyester, polyamide/polyester, polyester/polyether,polyurea/polyester, polyurea/polyester copolymers,polycaprolactone/urethane, in which the molecular weight of thepolycaprolactone blocks is between 300 and
 3000. 19. Stable aqueouscomposition according to claim 2, wherein said polymers containinggroups of different hydrophilicity intercalated outside the backbone arecopolymers of ethylene with vinylalcohol and/or with acrylic acid. 20.Stable aqueous composition according to claim 3, wherein said polymerscontaining groups of different hydrophilicity intercalated outside thebackbone are copolymers of ethylene with vinylalcohol and/or withacrylic acid.